Event Number 2961

Abstract: Neutrino-less double beta decay may answer essential open questions in neutrino physics. While double beta decay accompanied by the emission of two neutrinos is allowed by the standard model, the neutrino-less process requires neutrinos to be Majorana particles. Detecting this decay could determine the nature of neutrinos, the neutrino effective mass, and the mass hierarchy. The Enriched Xenon Observatory (EXO) is an experimental program searching for neutrino-less double beta decay in xenon-136. The first stage of this program, EXO-200, features 200 kg of liquid xenon. The detector, located at the Waste Isolation Pilot Plant in New Mexico, has been taking data for two years. EXO-200 detected for the first time two-neutrino double beta decay of xenon, the slowest process ever measured directly. Furthermore it set a strong limit on the rate of zero-neutrino double beta decay. I will describe EXO-200 as well as prospects for the future large-scale detector nEXO.